Final answer:
The least possible number of people between Dana and Alex is 8.
Step-by-step explanation:
To find the least possible number of people between Dana and Alex, we need to consider the positions of both Alex and Gina in the line.
Alex counts 13 people in front of him, so there are 13 people behind Alex. Gina counts 21 people between her and Dana.
Since there are already 13 people behind Alex, we can assume that Dana is one of those 21 people counted by Gina. Therefore, the least possible number of people between Dana and Alex is 21 - 13 = 8 people.